Valves, such as gate valves and chokes, in recent years are expected to operate in a corrosive atmosphere, to retain pressures such as 15,000 psig and to function at a wide range of temperatures, such as from 250.degree. F. to 20.degree. F. One of the difficulties encountered in such valves is the failure of the stem seal.
In some prior valves an elastomer has been used to energize the seal. The elastomers deteriorate with time as a result of the presence of H.sub.2 S, corrosion inhibitors, high temperatures, gas decompression, and compression set.
In other prior valve design, a stamped metal spring has been used to energize a polytetrafluoroethylene lip seal. The spring must be thin and weak to provide the desired flexibility. Therefor, the sealing lips must be sufficiently thin so that the spring can energize them properly. Such thin lips have poor wear resistance and at high temperature the polytetrafluoroethylene lips soften and are distorted by the edges of the spring resulting in seal failure.
The following U.S. patents disclose shaft and stem seals which may be pertinent with respect to the present invention: U.S. Pat. No. 4,410,189 discloses a shaft seal having a tapered load ring to wedge the sealing lip into sealing engagement with the surfaces to be sealed. U.S. Pat. No. 4,426,093 discloses a stem seal for a valve which is a cylindrical sleeve with spaced external circumferential cuts to enable the sleeve to act as a loose stack of washers in sealing. U.S. Pat. No. 3,787,060 discloses a stem seal having a wedge sleeve forced into the stem packing to ensure sealing against the stem and the inner wall of the housing bore. U.S. Pat. No. 4,262,690 discloses wedges used to move rings into position to prevent extrusion of sealing rings in a stack of sealing rings.